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- New Horizons observed Pluto\u2019s atmosphere in 2015 as \u201cthin.\u201d<\/strong> The spacecraft found a mostly nitrogen atmosphere for this dwarf planet.<\/li>\n
- And now we know the atmospheric pressure on Pluto decreased by 16%<\/strong> between mid-2021 and July 2023.<\/li>\n
- How do we know?<\/strong> Scientists detected the change while watching Pluto pass in front of distant stars, during what are called \u201coccultations.\u201d<\/li>\n<\/ul>\n
Pluto\u2019s atmosphere is thinning<\/h3>\n
On July 31, 2026, a team of scientists led by Amanda Sickafoose at the Planetary Science Institute in Tucson, Arizona, published peer-reviewed findings showing that Pluto\u2019s atmospheric pressure decreased by 16% between mid-2021 and July 2023. The team detected the change by observing Pluto occult, or pass in front of, distant stars. The researchers might have even detected the first signs of Pluto\u2019s coming atmospheric collapse<\/em>.<\/p>\n
Only one spacecraft from Earth has ever visited Pluto. That was New Horizons in 2015. It found that Pluto has an extremely thin, but hazy, atmosphere made mostly of nitrogen. But we knew before New Horizons that Pluto\u2019s atmosphere should thicken and thin in a 248-year cycle, as this tiny outer world (with its greatly elongated orbit) moves closer to and then farther from the sun. <\/p>\n
Pluto came closest to the sun on September 5, 1989. Then it was closer to the sun than Neptune\u2019s orbit. Now it is moving away from the sun, heading out to a colder part of the solar system. We know its atmosphere will thin out and freeze onto its surface.<\/p>\n
Pluto won\u2019t turn back towards the sun until the yeaer 2114. Until then, there\u2019s lots of time for scientists to study this little world in the colder part of its orbit.<\/p>\n
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\u2014 Planetary Science Institute | Discovery & Public Education in P\u2026 (@psi.edu.web.brid.gy) 2026-07-31T18:04:54.000Z<\/p>\n<\/blockquote>\n
Measuring Pluto\u2019s thinning atmosphere<\/h3>\n
The new study examined how Pluto\u2019s atmosphere has changed between 2017 and 2023. New Horizons\u2018 flyby of Pluto was in 2015. The researchers found that between the flyby and into 2021, Pluto\u2019s atmospheric pressure remained constant. No thinning yet.<\/p>\n
But then something changed. Between mid-2021 and July 2023, the atmospheric pressure decreased by 16%.<\/p>\n
![\"Black](\"https:\/\/earthsky.org\/upl\/2026\/08\/Pluto-haze-atmosphere-New-Horizons-July-14-2015.jpg\")
View larger. | This image from New Horizons on July 14, 2015 shows the hazes in Pluto\u2019s ultra-thin atmosphere. Image via NASA\/ Johns Hopkins University Applied Physics Laboratory\/ Southwest Research Institute.<\/figcaption><\/figure>\n Occultations provide clues<\/h3>\n
How did the researchers measure the atmosphere? They can do so when Pluto occults \u2013 passes in front of \u2013 a distant star. By measuring how the starlight changes, the researchers can get clues about Pluto\u2019s atmosphere.<\/p>\n
Even though Pluto is extremely far away from us, it casts its shadow on Earth during an occultation. Scientists in different parts of the world create maps of the shadow\u2019s path across Earth.<\/p>\n
Lead author Amanda Sickafoose at the Planetary Science Institute and her colleagues have observed 10 such occultations since 2017. The researchers could confirm their observations from multiple locations on Earth. Sickafoose said:<\/p>\n
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We often prefer to observe predicted occultations that have shadow paths over large observatories because that equipment and data have proven successful. Then, we try to improve those datasets by collaborating with local observers in the shadow paths.<\/p>\n<\/blockquote>\n
![\"Smiling](\"https:\/\/earthsky.org\/upl\/2026\/08\/Amanda-Sickafoose-Planetary-Science-Institute-1.jpg\")
Amanda Sickafoose at the Planetary Science Institute is the lead author of the new study about Pluto\u2019s thinning atmosphere. Image via Planetary Science Institute.<\/figcaption><\/figure>\n Brightness of the star<\/h3>\n
Pluto is extremely faint of course, since it is incredibly far away. This is why the brightness of the background star is so important. Scientists use various telescopes to measure the brightness of the star before, during and after the occultation.<\/p>\n
Despite the faintness of Pluto, its thin, hazy atmosphere bends the star\u2019s light enough to be detectable from Earth. Sickafoose said:<\/p>\n
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I\u2019m constantly amazed at how the simple technique of watching starlight dim and reappear allows us to study a thin atmosphere \u2013 a few millionths of the Earth\u2019s \u2013 on a world two-thirds the size of our moon and 30 times farther from the sun.<\/p>\n<\/blockquote>\n
Sickafoose concluded:<\/p>\n
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We\u2019re at a particularly interesting point for Pluto. Our work suggests that the atmosphere has recently started decreasing in pressure. I am hopeful that we\u2019ll be able to get more data in the next years to decades to specifically confirm or refute this trend.<\/p>\n<\/blockquote>\n
![\"Multi-colored](\"https:\/\/earthsky.org\/upl\/2022\/04\/Pluto-New-Horizons-July-14-2015.png\")
View larger. | When New Horizons arrived at Pluto in 2015, it found this large heart-shaped feature on the planet\u2019s surface. Pluto\u2019s \u201cheart\u201d measures approximately 1,000 miles (1,600 km) across. It\u2019s a vast plain of nitrogen ice. Image via NASA\/ JHUAPL\/ SwRI\/ The University of Arizona.<\/figcaption><\/figure>\n New Horizons sees Pluto\u2019s hazy atmosphere<\/h3>\n
NASA\u2019s New Horizons spacecraft saw Pluto\u2019s hazy atmosphere up close when it flew past the dwarf planet on July 14, 2026. You can clearly see the haze layers in the images the probe sent back to Earth. And the famous \u201cblue ring\u201d , at the top of this post, is particularly amazing. It shows Pluto backlit by the sun, with its atmosphere appearing a bright blue ring in the blackness of space.<\/p>\n
Last month, another study found that Pluto and Saturn\u2019s moon Titan both have the same mysterious molecule on their surfaces. And scientists don\u2019t know what it is yet. Interesting!<\/p>\n
Bottom line: Bottom line: Scientists detected that Pluto\u2019s atmosphere is thinning as it moves farther away from the sun in its orbit. They did so when Pluto passed in front of distant stars.<\/p>\n
Source: Changes in Pluto\u2019s Atmosphere Based on Stellar Occultation Data from 2017 to 2023<\/p>\n
Via Planetary Science Institute<\/p>\n
Read more: Titan and Pluto share same mysterious molecule: What is it?<\/p>\n
Read more: Will Pluto become a planet again? The ongoing debate<\/p>\n
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\n - And now we know the atmospheric pressure on Pluto decreased by 16%<\/strong> between mid-2021 and July 2023.<\/li>\n